1. Field of the Invention
This invention relates to input/output (I/O) devices for integrated circuits, and more particularly, to an I/O device for use on an integrated circuit to serve as a communication interface whose input/output characteristics is programmable after foundry to be matched to the external circuitry to which the IC chip is connected for use. The invention also relates to a self-control I/O device which can detect whether the I/O characteristics of the I/O device are matched to the external circuitry and, if not, automatically set the I/O device to the required I/O characteristics.
2. Description of Related Art
FIG. 1 is a schematic diagram showing the top view of a conventional IC chip. As shown, the layout area of the IC chip is partitioned into a center area 11, where the core functionality of the IC chip is provided, and an I/O area 12, where a plurality of I/O devices serving as a communication interface for the core circuitry of the IC chip to perform I/O functions with external circuitry is provided. These I/O devices are formed together with the core circuitry on the center area 11 in the foundry process for the IC chip.
FIG. 2 is a schematic diagram showing the inside structure of each of the above-mentioned I/O devices provided on the I/O area 12 in the IC chip 10 of FIG. 1. As shown, this I/O device includes an output buffer 21 and an input receiver 22, both of which are connected between the external circuitry and the core circuitry provided on the center area 11 of the IC chip 10 of FIG. 1. The output characteristic of the output buffer 21 and the input characteristic of the input receiver 22 are factory-set and fixedly built in the I/O component 20 during the foundry process in compliance with the particular external circuitry to which the IC 10 is to be connected for use. Once set, the I/O characteristics of the I/O component 20 cannot be changed.
FIG. 3 is a schematic diagram showing the various stages in a typical IC manufacturing process, which include design, photomasking, foundry, packaging, and system verification. If the I/O characteristics of an IC chip are mismatch to the external circuitry to which the IC chip is connected for use, that IC chip will fail to pass the system verification. The mismatch can be caused by several reasons as described below.
For the output buffer 21, the mismatch in its output characteristic can be caused by such factors as variable loading, system variation, mismatch in the specifications between the IC chip and the external circuitry, and noise, to name a few. For the input receiver 22, the mismatch in its input characteristic can be caused by such factors as a mismatch in CMOS/TTL (complementary metal-oxide semiconductor and transistor-transistor logic) pull-up/pull-down modes, whether a noise-immune Schmitt trigger is provided, and so on.
In the event of a mismatch in the I/O characteristic, since the I/O characteristics are factory-set and fixedly built in the I/O device, they cannot be changed thereafter to match the external circuitry. As a result, the IC chip may have to be discarded and new IC chips with matched I/O characteristics are to be manufactured. This will not only cause a waste in the semiconductor materials but cause a delay in the delivery of the ordered IC products to the customer, both of which would cause loss to the manufacturer.